1. Technical Field
The present invention relates in general to multi-stage pumps and, in particular, to a system, method and apparatus for an open shroud impeller and diffuser assembly for a multi-stage submersible pump.
2. Description of the Related Art
When an oil well is initially completed, the downhole pressure may be sufficient to force the well fluid up the well tubing string to the surface. The downhole pressure in some wells decreases, and some form of artificial lift is required to get the well fluid to the surface. One form of artificial lift is suspending an electric submersible pump (ESP) downhole, normally on the tubing string. The ESP provides the extra lift necessary for the well fluid to reach the surface. One type of ESP is a centrifugal pump. Centrifugal pumps have a series of impellers inside of a tubular housing, which are rotated by a drive shaft in order to propel fluids from the radial center of the pump towards the tubular housing enclosing the impellers.
The impellers have an inlet or an eye towards the radial center portion around the drive shaft. Spinning the impeller creates centrifugal forces on the fluid in the impeller. The centrifugal forces increase the velocity of the fluid in the impeller as the fluid is propelled towards the tubular housing. The height that the fluid would be able to travel in a passageway extending vertically from the exit of the impeller is the “head” generated from the impeller. A large amount of head is necessary in order to pump the well fluid to the surface. Either increasing the impeller diameter or increasing the number of impellers can increase the amount of head generated by a pump. The diameter of the impellers is limited by the diameter of the well assembly. Therefore, increasing the number of impellers is the common solution for downhole pumps in order to generate enough head to pump the well fluid to the surface.
The fluid enters a stationary diffuser after exiting the impeller. The fluid loses velocity in the diffuser because it is stationary. Decreasing the velocity of the fluid in the diffuser causes the pressure of the fluid to increase. The diffuser also redirects the fluid to the eye or inlet of the next impeller. Each impeller mounts directly to the drive shaft, but the diffusers slide over the drive shaft and land on the diffuser of the previous stage. Each impeller and diffuser is a “stage” in a pump. The pressure increase from one stage is additive to the amount of head created in the next stage. After enough stages, the cumulative pressure increase on the well fluid is large enough that head created in the last impeller pumps the well fluid to the surface. Thus, improved solutions for increasing the number of stages in a given length of well would be desirable.